A quick video demonstrating how to use drain rods to clear a blocked outside drain.
I purchased this set of rods from Screwfix and paid £22 at the time. They come as a set with 10 poles 90cm each so a total of 9m and the set also comes with a plunger and a hook attachment.
https://www.screwfix.com/p/bailey-19mm-black-drain-rod-set-9-14m/78472?tc=XB8&ds_kid=92700055262507126&ds_rl=1244066&gclid=Cj0KCQiA09eQBhCxARIsAAYRiynY1U9EyrkEXfKVPYKoH0J9TKIE2pDTjSICS91u-ft3-qaomjqWWQYaAixBEALw_wcB&gclsrc=aw.ds